This invention relates to polydioranosiloxane polyurea segmented copolymers and a process for making same.
Polydiorganosiloxane polymers have unique properties derived mainly from the physical and chemical characteristics of the siloxane bond. Typically, the outstanding properties of polydiorganosiloxane polymers include resistance to ultraviolet light, extremely low glass transition temperature, good thermal and oxidative stability, good permeability to many gases, very low surface energy, low index of refraction, good hydropnobicity, and good dielectric properties. They also have very good biocompatibility and are of great interest as biomaterials which can be used in the body in the presence of blood. Polydiorganosiloxane elastomers have been widely used because of these many excellent properties. But, their limited tear resistance and poor resistance to low polarity solvents have made them unsuitable in many other applications.
Elastomers possess the ability to recover their initial shape from deformation produced by an imposed force. Traditional polydiorganosiloxanes show elastomeric behavior only when they are chemically or physically crosslinked. Even extremely high molecular weight polydiorganosiloxane gums (greater than 500,000 grams per mole) exhibit cold flow when uncrosslinked. Thus, to be useful in most commercial applications, traditional polydiorganosiloxanes must be further filled with up to 50 weight percent fillers such as finely divided high surface area silica, fumed silica, titanium dioxide, alumina, zirconia, pigment-grade oxides, carbon blacks graphite, metal powders, clays, calcium carbonates, silicates, aluminates, fibrous fillers, and hollow glass or plastic microspheres, depending on the desired properties, for example, to maintain their mechanical strength and reduce swelling in solvents. Since polydiorganosiloxanes do not lose their mechanical strength as abruptly as other organic materials at elevated temperatures, they find particular use in high temperature applications.
For many uses such as in insulated wire, rods, channels, tubing, and similar products, polydiorganosiloxane compounds are extruded in standard rubber extrusion equipment. The extruded material must immediately be heated to set the form. Usually, hot-air vulcanization at 300-450xc2x0 C. or steam at 0.28-0.70 MPa (40-100 psi) for several minutes is needed. Final properties can be developed by oven curing or by continuous steam vulcanization.
Silicone based release coatings have been used commercially for some time, predominantly in such applications as release liners for adhesives. Generally, these materials are coated from solvent or a carrier and thermally crosslinked at high temperatures. Recently, silicone release technologies have been disclosed which include addition cure, cationic cure, and radiation cure systems as well as silicone-containing block copolymers which do not require curing. Some of these systems can be coated without solvent, e.g., by roll coating. Others can be coated from organic solvents or water. None of these systems are believed to be hot melt processable. Thus, there is still a need for a silicone-based release coating that is hot melt coatable while retaining the desirable release performance features of the previously mentioned materials.
Block copolymers have long been used to obtain desirable performance characteristics in various products such as elastomers, sealants, caulking compounds, and release coatings.
Physically crosslinked polydiorganosiloxane elastomers usually are segmented copolymers. The mechanical properties of an elastomer generally increase with the molecular weight of the polymer. The molecular weight often can be determined by inherent viscosity measurements. For some uncrosslinked systems, as the molecular weight increases, the polymer becomes less soluble and the inherent viscosity becomes more difficult to measure. The mechanical properties and inherent viscosities of the polydiorganosiloxane polymers can be substantially increased, while most of the desired polydiorganosiloxane properties are maintained, through controlled, solvent-based synthesis of AB, ABA, or (AB)n segmented polymers, with a soft polydiorganosiloxane component and a hard component of either a crystalline structure with a high melting point or an amorphous structure with a high glass transition temperature and include, for example, hard segments such as polystyrene, polyamide, polyurethane, polyimide, polyester, polycarbonate, polysulfone and epoxide.
Another class of polydiorganosiloxane segmented copolymers is polydiorganosiloxane polyurea segmented copolymers which may contain blocks other than polydiorganosiloxane or urea. These have some potential process economy advantages because their synthesis reaction is more rapid than those previously mentioned, requires no catalyst, and produces no by-products.
In producing polydiorganosiloxane polyurea segmented copolymers, monofunctional reaction impurities in the polydiorganosiloxane diamine precursor can prematurely terminate the chain extension reaction and limit the attainment of optimum molecular weight and tensile strength of the polymer. Because the early processes for making the polydiorganosiloxane diamines resulted in increasing levels of monofunctional impurities with increasing molecular weight, it was not possible to achieve elastomers having satisfactory mechanical properties for most elastomer or adhesive applications. More recently, processes have been developed which produce materials with low levels of impurities over a wide range of polydiorganosiloxane diamine molecular weights. With this chemistry, polydiorganosiloxane polyurea segmented copolymers have been obtained having inherent viscosities of over 0.8 g/dL measured at 30xc2x0 C. (using a Canon-Fenske viscometer with chloroform solution at a concentration of 0.4 g/dL) through the use of chain extenders to increase the non-silicone content.
Solution polymerized polydiorganosiloxane polyurea elastomers which do not require a cure step have been described. However, because these compositions are made in solvent, they can have costly handling procedures.
Continuous melt polymerization processes are advantageous and have been used to make compositions such as polyurethane elastomers and acrylate pressure sensitive adhesives. A continuous melt polymerization process for producing polyetherimides, which can contain polydiorganosiloxane segments, has also been described. Recently polyurethane resins have been described which use polydiorganosiloxane urea segments to prevent blocking of film formed from the resin. However, levels of reactive polydiorganosiloxane in the compositions were small, for example, less than 15 weight percent, and potential incomplete incorporation of the polydiorganosiloxane into the backbone was not detrimental since easy release was the intent. Unincorporated polydiorganosiloxane oil can, however, act as a plasticizing agent in elastomers to reduce tensile strength or detackify and reduce shear properties of pressure-sensitive adhesives. This unincorporated oil can also bloom to the surface of an elastomer or adhesive and contaminate other surfaces with which it is in contact.
Briefly, in one aspect of the present invention melt-processable polydiorganosiloxane polyurea segmented copolymer compositions are provided wherein such compositions comprise alternating soft polydiorganosiloxane units, and hard polyisocyanate residue units, (wherein the polyisocyanate residue is the polyisocyanate minus the xe2x80x94NCO groups), and optionally, soft and/or hard organic polyamine units, and such that the residues of the amine and isocyanate units are connected together by urea linkages. Compositions of the present invention typically have inherent viscosities of at least 0.8 dL/g, or are essentially insoluble in common organic solvents such as, for example, chloroform, tetrahydrofuran, dimethyl formamide, toluene, isopropyl alcohol, and combinations thereof
The present invention also provides polydiorganosiloxane polyurea segmented copolymer compositions comprising the reaction product of
(a) at least one polyamine, wherein the polyamine comprises at least one polydiorganosiloxane diamine, or a mixture of at least one polydiorganosiloxane diamine and at least one organic polyamine, and
(b) at least one polyisocyanate,
wherein the mol ratio of isocyanate to polyamine is between 0.9:1 and 0.95:1 or between 1.05:1 and about 1.3:1.
The polydiorganosiloxane polyurea segmented copolymers of the invention can be represented by the repeating unit: 
wherein:
each R is a moiety that independently is an alkyl moiety preferably having about 1 to 12 carbon atoms and may be substituted with, for example, trifluroalkyl or vinyl groups, a vinyl radical or higher alkenyl radical preferably represented by the formula xe2x80x94R2(CH2)aCHxe2x95x90CH2 wherein R2 is xe2x80x94(CH2)bxe2x80x94 or xe2x80x94(CH2)cCHxe2x95x90CHxe2x80x94 and a is 1, 2 or 3; b is 0, 3 or 6; and c is 3, 4 or 5, a cycloalkyl moiety having about 6 to 12 carbon atoms and may be substituted with alkyl, fluoroalkyl, and vinyl groups, or an aryl moiety preferably having about 6 to 20 carbon atoms and may be substituted with, for example, alkyl, cycloalkyl, fluoroalkyl and vinyl groups or R is a perfluoroalkyl group as described in U.S. Pat. No. 5,028,679, wherein such description is incorporated herein by reference, a fluorine-containing group, as described in U.S. Pat. No. 5,236,997, wherein such description is incorporated herein by reference, or a perfluoroether-containing group, as described in U.S. Pat. Nos. 4,900,474 and 5,118,775, wherein such descriptions are incorporated herein by reference; preferably at least 50% of the R moieties are methyl radicals with the balance being monovalent alkyl or substituted alkyl radicals having 1 to 12 carbon atoms, alkenylene radicals, phenyl radicals, or substituted phenyl radicals;
each Z is a polyvalent radical that is an arylene radical or an aralkylene radical preferably having from about 6 to 20 carbon atoms, an alkylene or cycloalkylene radical preferably having from about 6 to 20 carbon atoms, preferably Z is 2,6-tolylene, 4,4xe2x80x2-methylenediphenylene, 3,3xe2x80x2-dimethoxy-4,4xe2x80x2-biphenylene, tetramethyl-m-xylylene, 4,4xe2x80x2-methylenedicyclohexylene, 3,5,5-trimethyl-3-methylenecyclohexylene, 1,6-hexamethylene, 1,4-cyclohexylene, 2,2,4-trimethylhexylene and mixtures thereof;
each Y is a polyvalent radical that independently is an alkylene radical of 1 to 10 carbon atoms, an aralkylene radical or an arylene radical preferably having 6 to 20 carbon atoms;
each D is selected from the group consisting of hydrogen, an alkyl radical of 1 to 10 carbon atoms, phenyl, and a radical that completes a ring structure including B or Y to form a heterocycle;
B is a polyvalent radical selected from the group consisting of alkylene, aralkylene, cycloalkylene, phenylene, polyalkylene oxide, including for example, polyethylene oxide, polypropylene oxide, polytetramcthylene oxide, and copolymers and mixtures thereof;
m is a number that is 0 to about 1000;
n is a number that is equal to or greater than 1; and
p is a number that is about 10 or larger, preferably about 15 to 2000, more preferably about 30 to 1500.
In the use of polyisocyanates (Z is a radical of functionality greater than 2) and polyamines (B is a radical of functionality greater than 2), the structure of Formula I will be modified to reflect branching at the polymer backbone.
Polymers of the present invention typically have an inherent viscosity of at least about 0.8 dUg or are essentially insoluble in common organic solvents.
The compositions of the invention may further comprise fillers, tackifying agents, resins, pigments, stabilizers, plasticizers, and the like.
The polydiorganosiloxane polyurea segmented copolymers of the present invention have good mechanical properties even when unfilled and exhibit excellent physical properties typically associated with polysiloxanes, such as low glass transition temperature, transparency moderate resistance to ultraviolet light, low surface energy and hydrophobicity, good dielectric properties, and high permneability to many gases. Additionally, the polydiorganosiloxane polyurea segmented copolymers of the invention have moderate thermal and oxidative stabilities, have higher inherent viscosities than were previously obtainable, and are amenable to melt processing after polymerization. Further, some of the polydiorganosiloxane polyurea segmented copolymers of the invention are more resistant to swelling and degradation by hydrocarbon solvents than those previously obtainable. Also, some of the polydiorganosiloxane polyurea segmented copolymers of the invention are elastomeric materials that exhibit surprisingly low melt flow viscosities, and abrupt solidification at a temperature below melt flow conditions. In addition, some polydiorganosiloxane polyurea segmented copolymers of the present invention have an enhanced range of ultimate properties due to the expanded compositions available when organic polyamines are used with the polydiorganosiloxane diamines and polyisocyanates. These compositions vary over a wide range of choices and percentage incorporation for these reactants and afford polydiorganosiloxane polyurea segmented copolymers with tailorable properties, Such properties can include peel release levels, printability, tensile and tear strengths, moisture vapor transmission rates, as well as molecular structures and compositions not hereto available via solvent-based synthetic techniques.
In another aspect, the present invention provides a process for making the polydiorganosiloxane polyurea segmented copolymers comprising the steps of
(a) continuously providing reactants to a reactor, wherein the reactants comprise at least one polyisocyanate and at least one polyamine, wherein the polyamine is at least one polydiorganosiloxane diamine or a mixture of at least one polydiorganosiloxane diamine and at least one organic polyamine,
(b) mixing the reactants in the reactor,
(c) allowing the reactants to react to form a polydiorganosiloxane polyurea copolymer, and
(d) conveying the polymer from the reactor.
Preferred polyisocyanates useful in the process of the present invention can be represented by the formula:
xe2x80x83OCNxe2x80x94Zxe2x80x94NCOxe2x80x83xe2x80x83(II)
wherein Z is defined as above.
Polydiorganosiloxane diarines useful in the process of the present invention can be represented by the formula 
wherein each of R, Y, D, and p are defined as above. Generally, the number average molecular weight of the polydiorganosiloxane diamines useful in the present invention are greater than about 700.
The process is substantially solventless. Generally, no solvent is needed to carry out the reaction, making the process more environmentally friendly than previous processes for making polydiorganosiloxane polyurea segmented copolymers as well as providing unique properties to many of the polydiorgano-siloxane polyurea segmented copolymers. Small amounts of solvent may be present, if necessary, to control the flow of solid isocyanates, high viscosity diisocyanates, or low amounts of diisocyanates, or for controlled addition of adjuvants such as tackifying resins, pigments, crosslinking agents, plasticizers fillers, and stabilizing agents, or to reduce their viscosity.
Advantageously, the essentially solventless and continuous process enables optimization of the properties of final materials by adjusting the isocyanate to amine ratio below and, surprisingly, well above 1:1. Unexpectedly, strong, extrudable materials are obtained, some of which have uniquely superior mechanical and Theological properties over those obtainable by conventional solvent polymerization processes. An additional benefit of the continuous, essentially solventless process of the present invention is the ability to extrude the polydiorganosiloxane polyurea segmented copolymer into a variety of shapes such as, for example, films, fibers, pellets, sheets, slabs, and tubing, directly after polymerization. This minimizes the heat and shear history of the polymer which can reduce performance characteristics due to possible degradation of the polymer.
Generally, the inherent viscosity of the resultant polydiorganosiloxane polyurea segmented copolymers increases with increasing polydiorganosiloxane diamine molecular weight. The inherent viscosities of the copolymers can be altered by the selection of the appropriate isocyanate to amine ratios and process conditions. Polydiorganosiloxane polyurea segmented copolymers having inherent viscosities greater than can be produced using conventional solution polymerization processes are achievable.
Using the process of the present invention, molecular weights can be achieved such that the copolymer is essentially insoluble in common organic
Using the process of the present invention, molecular weights can be achieved such that the copolymer is essentially insoluble in common organic solvents. Further the process of the present invention, being a continuous bulk polymerization process, provides the ability to make high molecular weight compositions which are not obtainable by conventional solution polymerization due to the high viscosity or gel formation of the forming polymer in the solvent medium.
Polydiorganosiloxane diamines useful in the present invention are any that fall within Formula III above and include those having number average molecular weights in the range of about 700 to 150,000, more preferably greater than 1600. Preferred silicone diamines are substantially pure polydiorganosiloxane diamines prepared as described in U.S. Pat. No. 5,214,119 wherein such description is incorporated herein by reference. Polydiorganosiloxane diamines having such high purity are prepared from the reaction of cyclic organosilanes and bis(aminoalkyl)disiloxanes utilizing an anhydrous amino alkyl functional silanolate catalyst such as tetramethylammonium 3-aminopropyldimethylsilanolate, preferably in an amount less than 0.15 weight percent based on the weight of the total amount of cyclic organosiloxane with the reaction run in two stages.
Particularly preferred polydiorganosiloxane diamines are prepared using cesium and rubidium catalysts. The preparation of polydiorganosiloxane diamine includes combining under reaction conditions
(1) an anine functional endblocker represented by the formula 
wherein:
each R, D and Y are defined as above, and
x is an integer of about 1 to 150;
(2) sufficient cyclic siloxane to obtain a polydiorganosiloxane diamine having a number average molecular weight greater than the molecular weight of the endblocker; and
(3) a catalytically effective amount of cesium hydroxide, rubidium hydroxide, cesium silanolate, rubidium silanolate, cesium polysiloxanolate, rubidium polysiloxanolate, and mixtures thereof The reaction is continued until substantially all of the amine functional endblocker is consumed.
The reaction is then terminated by adding a volatile organic acid to form a mixture of a polydiorganosiloxane diamine usually having greater than about 0.01 weight percent silanol impurities and one or more of the following: a cesium salt of the organic acid, a rubidium salt of the organic acid, or both such that there is a small molar excess of organic acid in relation to catalyst. The silanol groups of the reaction product are then condensed under reaction conditions to form polydiorganosiloxane diamine having less than or equal to about 0.01 weight percent silanol impurities while the unreacted cyclic siloxane is stripped. Optionally, the salt is removed by subsequent filtration.
Examples of polydiorganosiloxane diamines useful in the present invention include but are not limited to polydimethylsiloxane diamine, polydiphenylsiloxane diamine, polytrifluoropropylmethylsiloxane diamine, polyphenylmethylsiloxane diamine, polydiethylsiloxane diamine, polydivinylsiloxane diamine, polyvinylmethylsiloxane diamine, poly(5-hexenyl)methylsiloxane diamine, copolymers and mixtures thereof.
Examples of organic polyamines useful in the present invention include but are not limited to polyoxyalkylene diamines such as D-230, -400, -2000, -4000, BU-700, ED-2001, EDR-148 available from Huntsman, polyoxyalkylene triamines such as T-3000 and T-5000 available from Huntsman, and polyalkylenes such as Dytek A and Dytek EP available from DuPont.
Different polyisocyanates in the reaction will modify the properties of the polydiorganosiloxane polyurea segmented copolymer. For example, if a polycarbodiimide-modified diphenylmethane diisocyanate, such as ISONATE(trademark) 143L, available from Dow Chemical Co., is used, the resulting polydiorganosiloxane polyurea segmented copolymer has enhanced solvent resistance when compared with copolymers prepared from other diisocyanates. If tetramethyl-m-xylylene diisocyanate is used, the resulting segmented copolymer has a very low melt viscosity that makes it particularly useful for injection molding.
Any polyisocyanate that can react with a polyamine, and in particular with polydiorganosiloxane diamine of Formula III can be used in the present invention. Examples of such diisocyanates include, but are not limited to, aromatic diisocyanates, such as 2,6-toluene diisocyanate, 2,5-toluene diisocyanate, 2,4-toluene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, methylene bis(o-chlorophenyl diisocyanate), methylenediphenylene-4,4xe2x80x2-diisocyanate, polycarbodiimide-modified methylenediphenylene diisocyanate, (4,4xe2x80x2-diisocyanato-3,3xe2x80x2,5,5xe2x80x2-tetraethyl) diphenylmethane, 4,4xe2x80x2-diisocyanato-3,3xe2x80x2-dimethoxybiphenyl(odianisidine diisocyanate), 5-chloro-2,4-toluene diisocyanate, 1-chloromethyl-2,4-diisocyanato benzene, aromatic-aliphatic diisocyanates such as m-xylylene diisocyanate, tetramethyl-m-xylylene diisocyanate, aliphatic diisocyanates, such as 1,4-diisocyanatobutane, 1,6-diisocyanatohexane, 1,12-diispcyanatododecane, 2-methyl-1,5-diisocyanatopentane, and cycloaliphatic diisocyanates such as methylenedicyclohexylene-4,4xe2x80x2-diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate), 2,2,4-trimethylhexyl diisocyanate, and cyclohexylene-1,4-diisocyanate and mixtures thereof.
Preferred diisocyanates include 2,6-toluene diisocyanate, methylenediphenylene-4,4xe2x80x2-diisocyanate, polycarbodiimide-modified methylenediphenyl diisocyanate, 4,4xe2x80x2-diisocyanato-3,3xe2x80x2-dimethoxybiphenyl(odianisidine diisocyanate), tetramethyl-m-xylylene diisocyanate, methylenedicyclohexylene-4,4xe2x80x2-diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate(isophorone diisocyanate), 1,6-diisocyanatohexane, 2,2,4-trimethylhexyl diisocyanate, and cyclohexylene-1,4-diisocyanate.
Particularly preferred is tetramethyl-m-xylylene diisocyanate. Polydiorganosiloxane polyurea segmented copolymers produced using tetraniethyl-m-xylylene diisocyanate generally have lower melt viscosities than similar copolymers produced using other diisocyanates, and higher modulus.
Any triisocyanate that can react with a polyamine, and in particular with polydiorganosiloxane diamine of Formula III, can be used in the present invention. Examples of such triisocyanates include, but are not limited to, polyfunctional isocyanates, such as those produced from biurets, isocyanurates, adducts and the like. Some commercially available polyisocyanates include portions of the DESMODUR(trademark) and MONDUR(trademark) series from Bayer and the PAPI(trademark) series of Dow Plastics.
Preferred triisocyanates include DESMODUR(trademark) N-3300 and MONDUR(trademark) 489.
Relative amounts of amine and isocyanate can be varied over a much broader range than those produced by previous methods. Molar ratios of isocyanate to amine continuously provided to the reactor are preferably from about 0.9:1 to 1.3:1, more preferably 1:1 to 1.2:1.
Once the reaction of the polyisocyanate with the polyamine has occurred, active hydrogens in the urea linkage may still be available for reaction with excess isocyanate. By increasing the ratio of isocyanate to amine, the formation of biuret moieties may be facilitated, especially at higher temperatures, resulting in branched or crosslinked polymer. Low to moderate amounts of biuret formation can be advantageous to shear properties and solvent resistance.
The composition of the present invention may also optionally contain various fillers and other property modifiers. Fillers such as fumed silica, carbon fibers, carbon black, glass beads, glass bubbles, glass fibers, mineral fibers, clay particles, organic fibers, e.g., nylon, KEVLAR(trademark), metal particles, and the like can be added in amounts up to about 50 parts per 100 parts of polyorganosiloxane urea segmented polymer and silicate resin, provided that if and when incorporated, such additives are not detrimental to the function and functionality of the final polymer product. Other additives such as dyes, pigments, flame retardants, stabilizers, antioxidants, compatibilizers, antimicrobial agents such as zinc oxide, electrical conductors, thermal conductors such as aluminum oxide, boron nitride, aluminum nitride, and nickel particles, and the like can be blended into these systems in amounts of from about 1 to 50 volume percent of the composition.
In the process of the present invention, reactants, including at least one polyamine, wherein such polyamine is at least one polydiorganosiloxane diamine or a mixture of at least one polydiorganosiloxane diamine and at least one organic polyamine and at least one polyisocyanate diamine are mixed in a reactor and allowed to react to form the polydiorganosiloxane polyurea segmented copolymer that can then be removed from the reaction vessel.
In the process of the invention, the following reaction occurs: 
Properties of the compositions of the present invention result from the copolymer molecular weight and architecture. Flexibility of the process of the present invention leads to interesting materials, some of which, though they maynot be fully soluble in solvents for inherent viscosity or molecular weight determination, may nevertheless be quite useful materials in terms of physical properties and can still be extrudable. One skilled in the art can expect the optimum material for a particular application to be a function of isocyanate-to-amine ratio, polyisocyanate and polyamine architecture, order of reactant addition, mixing speed, temperature, reactor throughput, reactor configuration and size, residence time, residence time distribution, and whether any fillers, additives, or property modifiers are added. This process allows the freedom to vary the molecular weight and architecture over quite a wide range, thus enabling one to tailor the properties to suit a variety of applications. The polydiorganosiloxane polyamine component employed to prepare polydiorganosiloxane polyurea segmented copolymers of this invention provides a means of adjusting the modulus of the resultant copolymer. In general, high molecular weight polydiorganosiloxane diamines provide copolymers of lower modulus, whereas low molecular weight polydiorganosiloxane diamines provide higher polydiorganosiloxane polyurea segmented copolymers of high modulus.
Any reactor that can provide intimate mixing of polyamine and polyisocyanate and the reaction products thereof is suitable for use in the invention. The reaction may be carried out as a batch process using, for example, a flask equipped with a mechanical stirrer, provided the product of the reaction has a sufficiently low viscosity at the processing temperature to permit mixing, or as a continuous process using, for example, a single screw or twin screw extruder. Preferably, the reactor is a wiped surface counter-rotating or co-rotating twin screw extruder.
The temperature in the reactor should be sufficient to permit the reaction between the polyisocyanate and the polyamine to occur. The temperature should also be sufficient to permit conveying of the materials through the reactor, and any subsequent processing equipment such as, for example, feedblocks and dies. For conveying the reacted material, the temperature should preferably be in the range of about 140 to 250xc2x0 C., more preferably in the range of about 160 to 220xc2x0 C. Residence time in the reactor typically varies from about 5 seconds to 8 minutes, more typically from about 15 seconds to 3 minutes.
The residence time depends on several parameters, including, for example, the length to diameter ratio of the reactor, mixing rates, overall flowrates, reactants, and the need to blend in additional materials. For materials involving reaction with minimal or no blending of a nonreactive component, the reaction can easily take place in as little as 5:1 length to diameter units of a twin screw extruder.
When a wiped surface reactor is used, relatively close clearances between the screw flight lands and the barrel are preferred, with this value typically lying between 0.1 to about 2 mm. The screws utilized are preferably fully or partially intermeshing or fully or partially wiped in the zones where a substantial portion of the reaction takes place.
Because of the rapid reaction that occurs between the polyamine and the polyisocyanate, both materials are preferably fed into an extruder at unvarying rates, particularly when using higher molecular weight polyamines, that is, with number average molecular weights of about 50,000 and higher. Such feeding rates generally reduce undesirable variability of the final product.
One method of insuring the continuous feeding into the extruder when a very low flow polyisocyanate stream is used is to allow the polyisocyanate feed line to touch or very nearly touch the passing threads of the screws. Another method would be to utilize a continuous spray injection device that produces a continuous stream of fine droplets of polyisocyanates into the reactor.
Typically, in formulating polydiorganosiloxane polyurea segmented block copolymers with additives such as tackifying resins, inorganic fillers, or other materials essentially non-reactive with the polydiorganosiloxane polyurea segmented copolymer reactants, the additives to be blended are added further downstream in the reactor after a substantial portion of the reaction of the polyamine and polyisocyanate has taken place.
However, the various reactants and additives can be added in any order provided the addition of an additive does not interfere with the reaction of the reactants. For instance, an additive that is particularly reactive with a polyisocyanate reactant typically would not be added until after the reaction of the polyisocyanate with a polyamine reactant. Further, the reactants can be added simultaneously or sequentially into the reactor and in any sequential order. For example, the polyisocyanate stream can be the first component added into the reactor in a manner such as mentioned above. Polyamine can then be added downstream in the reactor. Alternately, the polyisocyanate stream can also be added after the polyamine has been introduced into the reactor.
The process of the present invention has several advantages over conventional solution polymerization processes for making polydiorganosiloxane polyurea segmented copolymers such as (1) the ability to vary the isocyanate to amine ratio to obtain materials with properties superior to solution polymerized materials, (2) the capability of polymerizing high molecular weight compositions that cannot be easily produced using solution polymerization, (3) the ability to directly produce shaped articles with reduced heat histories, (4) the ability to more easily blend in fillers, tackifying resins, plasticizers, and other property modifiers, and (5) the elimination of solvent.
The flexibility of altering the isocyanate to amine ratio in the continuous process is a distinct advantage. This ratio can be varied above and below the theoretical value of 1:1 quite easily. In solution, ratios much above about 1.05:1 and below 0.95:1 yield lower molecular weight copolymer. In the process of the present invention, polydiorganosiloxane polyurea segmented copolymers with ratios up to as high as 1.3:1, depending upon the titrated number average molecular weight of the polydiorganosiloxane diamine, can be produced. Such polymers possess inherent viscosities well above those made with conventional solution processes but can still be melt processed. These polymers can also possess superior mechanical properties when compared to solution polymerized copolymers. At some ratios, resultant polymers can become insoluble, precluding the possibility of inherent viscosity determination, but the material can be melt processable and possesses high strength.
The ability to make high molecular weight compositions that cannot be produced by solution polymerization due to the insolubility of the forming polymer in the solvent medium, leads to useful, unique compositions. When the chain extension of the polyamine is carried out in solution with certain polyisocyanates such as polycarbodiimide-modified diphenylmethane diisocyanate, available, for example, from Dow Chemical Co. as ISONATE(trademark) 143L, newly forming polymer may precipitate out of solution, thus not enabling the formation of high molecular weight copolymer. When this composition is prepared using the solventless method of the present invention, high strength solvent resistant materials are formed. In a similar manner, materials made from a mixture of two widely dissimilar molecular weights of polyamine polymerized with a polyisocyanate using the solventless process of the present invention can be made with high inherent viscosities.
In general, long exposure to heat degrades polydiorganosiloxane polyurea segmented copolymers and leads to a degradation of physical properties. The degradation experienced by many of the solution polymerized polydiorganosiloxane polyurea segmented copolymers upon drying and subsequent hot melt extrusion is also overcome by the continuous process of the present invention because reactively extruded polydiorganosiloxane polyurea segmented copolymers can be extruded directly from the polymerization zone through a die to form shaped articles such as tubing and films without the additional heat history associated with solvent removal and the subsequent polymer reheating.
The ability to eliminate the presence of solvent during the reaction of polyamine and polyisocyanate yields a much more efficient reaction. The average residence time using the process of the present invention is typically 10 to 1000 times shorter than that required in solution polymerization. A small amount of non-reactive solvent can be added, if necessary, for example, from about 0.5% up to about 5% of the total composition, in this process either as a carrier for injecting otherwise solid materials or in order to increase stability of an otherwise low flowrate stream of material into the reaction chamber.
The objects, features and advantages of the present invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention. All materials are commercially available or known to those skilled in the art unless otherwise stated or apparent. In the examples all parts and percentages are by weight unless otherwise indicated. All molecular weights reported are number average molecular weights in grams/mol.
Titration of Polydiorganosiloxane and Organic Polyamines
The actual number average molecular weight of polydiorganosiloxane or organic polyamines were determined by the following acid titration. Sufficient diamine to yield about 1 milliequivalent of amine is dissolved in 50/50 tetrahydrofuran/isopropyl alcohol to form a 10% solution, This solution is titrated with 0.1N hydrochloric acid with bromophenyl blue as an indicator to determine number average molecular weight. However, when the diamines were polydiorganosiloxane diamines, the molecular weights of these diamines were dependent on the exact ratio of the reactants used in the diamine synthesis and the extent of stripping cyclic siloxanes. Remaining cyclics are diluents which increase the apparent molecular weight of polydiorganosiloxane diamine.
Polydimethylsilaxane Diamine A
A mixture of 4.32 parts bis(3-aminopropyl)tetramethyl disiloxane and 95.68 parts octamethylcyclotetrasiloxane was placed in a batch reactor and purged with nitrogen for 20 minutes. The mixture was then heated in the reactor to 150xc2x0 C. Catalyst, 100 ppm of 50% aqueous cesium hydroxide, was added and heating continued for 6 hours until the bis(3-aminopropyl) tetramethyl disiloxane had been consumed. The reaction mixture was cooled to 90xc2x0 C., neutralized with excess acetic acid in the presence of some triethylamine, and heated under high vacuum to remove cyclic siloxanes over a period of at least five hours. The material was cooled to ambient temperature, filtered to remove any cesium acetate which had formed, and titrated with 0.1N hydrochloric acid to determine number average molecular weight. Six lots of Polydimethylsiloxane Diamine A were made using this procedure. The molecular weights were Lot 1: 5280, Lot 2: 5570, Lot 3: 5330, Lot 4: 5310, Lot 5: 5270, and Lot 6: 5350.
Polydimethylsiloxane Diamine B
Polydimethylsiloxane diamine was prepared as described for Polydimethylsiloxane Diamine A except 2.16 parts bis(3-aminopropyl)tetramethyl disiloxane and 97.84 parts octamethylcyclotetrasiloxane were used. Two lots were made using this procedure. The molecular weights were Lot 1: 10,700 and Lot 2: 10,500.
Polydimethylsiloxane Diamine C
A mixture of 21.75 parts polydimethylsiloxane diamine A and 78.25 parts octamethylcyclotetrasiloxane was placed in a batch reactor, purged with nitrogen for 20 minutes and then heated in the reactor to 150xc2x0 C. Catalyst, 100 ppm of 50% aqueous cesium hydroxide, was added and heating continued for 3 hours until equilibrium concentration of cyclic siloxanes was observed by gas chromatography. The reaction mixture was cooled to 90xc2x0 C., neutralized with excess acetic acid in the presence of some triethylamine, and heated under high vacuum to remove cyclic siloxanes over a period of at least 5 hours. The material was cooled to ambient temperature, filtered, and acid titrated to determine the number average molecular weight. Two lots of Polydimethylsiloxane Diamine C were made using this procedure. The molecular weights were Lot 1: 22,300 and Lot 2: 17,000.
Polydimnethylsiloxane Diamine D
Polydimethylsiloxane diamine was prepared as described for Polydimethylsiloxane Diamine C except 12.43 parts Polydiorganosiloxane Diamne A and 87.57 parts octamethylcyclotetrasiloxane were used. Two lots were prepared. The molecular weights were Lot 1: 37,800, and Lot 2: 34,800.
Polydimethylsiloxane Diamine E
Polydimethylsiloxane diamine was prepared as described for Polydimethylsiloxane Diamine C except that 8.7 parts Polydimethylsiloxane Diamine A and 91.3 parts octamethylcyclotetrasiloxane were used. Two Lots were prepared. The molecular weights of the thus-produced Polydimethylsiloxane Diamine E were Lot 1: 58,700 and Lot 2: 50,200.
Polydimethylsiloxane Diamine F
Polydimethylsiloxane diamine was prepared as described for Polydimethylsiloxane Diamine C except that 4.35 parts Polydimethylsiloxane Diamine A and 95.65 parts octamethylcyclotetrasiloxane were used. The molecular weight of this Polydimethylsiloxane Diamine F was 105,000.
Polytrifluoropropylmethyldimethylsiloxane Diamine G
Polydimethylsiloxane diamine containing 10 mol % trifluoropropylmethyl and 90 mol % dimethylsiloxane units was made as described for the preparation of Polydimethylsiloxane Diamine A, except 8.70 parts (3,3,3trifluoropropyl)-methylcyclosiloxane (Petrarch catalog number T2844), and 4.35 parts bis(3-aminopropyl)tetramethyl disiloxane and 86.96 parts octamethylcyclotetrasiloxane were used. The molecular weight of this Polytrifluoropropylmethyl-dimethylsiloxane Diamine G was 5440.
Polydimethylsiloxane Diamine H
Polydimethylsiloxane diamine was prepared by placing in a batch reactor under nitrogen purge and with stirring 1.98 parts bis(3-aminopropyl)tetramethyldisoloxane and 9.88 parts octamethylcyclotetrasiloxane. The mixture was heated to 91xc2x0 C. and a trace (about 0.15 parts) of 3-aminopropyldimethyltetramethylammonium silanolate catalyst was added. To the resultant mixture was added dropwise over a 5 hour period 88.0 parts octamethylcyclotetrasiloxane. The reaction mixture was maintained at 91xc2x0 C. for an additional 7 hours and was then heated to 149xc2x0 C. for 30 minutes to decompose the catalyst. The product was then stripped at 91xc2x0 C. and 2700 N/m2 (2700 Pa) for about 120 minutes to remove volatile materials. The molecular weight of the resulting Polydimethylsiloxane Diamine H was 9970.
Polydimethylsiloaxane Diamine I
Polydimethylsiloxane diamine was prepared as described for Polydimethylsiloxane Diamine H except 4.42 parts bis(3-aminopropyl)tetramethyldisoloxane and 22.25 parts octamethylcyclotetrasiloxane were initially placed in the reactor. After heating, 0.03 parts 3-aminopropyldimethyltetramethylammonium silanolate catalyst, and 73.30 parts octamethylcyclotetrasiloxane were added. Two lots of this Polydimethylsiloxane Diamine I were prepared. The molecular weights were Lot 1: 4930 and Lot 2: 5260.
Polydiphenyldimedhylsilaxane Diamine J
To a 3-necked round bottom flask fit with mechanical stirrer, static nitrogen atmosphere, oil heating bath, thermometer, and reflux condenser, were added 75.1 parts octamethylcyclotetrasiloxane, 22.43 parts octaphenylcyclotetrasiloxane, and 2.48 parts bis(3-aminopropyl)tetramethyldisiloxane. Under static nitrogen atmosphere, the reactants were heated to 150xc2x0 C. and degassed under aspirator vacuum for 30 seconds before restoring static nitrogen atmosphere. A charge of 0.02 parts cesium hydroxide solution (50% aqueous) was added to the flask and heating continued for 16 hours at 150xc2x0 C. The flask was cooled to ambient temperature and then 2 mL triethylamine and 0.38 ML acetic acid were added. With good agitation flask was placed under a vacuum of 100 N/M2 (100 Pa), heated to 150xc2x0 C., and maintained at 150xc2x0 C. for 5 hours to remove volatile materials. After 5 hours heat was removed and contents cooled to ambient temperature. Two lots of Polydiphenyldimethylsiloxane Diamine J were prepared. The molecular weights were Lot 1xe2x80x949330 and Lot 2xe2x80x949620.
In the following examples, all polyisocyanates and organic polyamines were used as received and the isocyanate to amine ratios were calculated using the polyisocyanate molecular weight reported by the polyisocyanate supplier and the polydiorganosiloxane and organic polyamine molecular weights, wherein the molecular weights were determined by acid titration and/or supplied by the supplier.
The following test methods were used to characterize the polydiorganosiloxane polyurea segmented copolymers produced in the following examples:
Inherent Viscosity
Average inherent viscosities (IV) were measured at 30xc2x0 C. using a Canon-Fenske viscometer (Model No. 50 P296) in a chloroform solution at 30xc2x0 C. at a concentration of between 0.18 and 0.26 g/dL. Inherent viscosities of the materials of the invention were found to be essentially independent of concentration in the range of 0.1 to 0.4 g/dL. The average inherent viscosities were averaged over 3 or more runs. Any variations for determining average inherent viscosities are set forth in specific Examples.
Gel Permeation Chromatography
The weight average and number average molecular weights of selected polydimethylsiloxane polyurea segmented copolymers were determined via gel permeation chromatography with a HP 1090 Chronatograph equipped with a HP 1037A Refractive Index detector, a Waters 590 pump, a Waters Wisp auto-injector and a Kariba column oven at room temperature. The copolymer was dissolved in DMF w/v 0.05% LiBr at 15 mg/mL, filtered with a 0.2 micrometer nylon filter, and 100 microliters injected into a Jordi Mixed Bed column. The elution rate was 0.5 mL/min in DMF+0.05% w/v LiBr. Calibration was based on polystyrene standards from Pressure Chemical Company, Pittsburgh, Pa. Reported molecular weights are the polystyrene equivalents.
Mechanical Properties
The polydiorganosiloxane polyurea segmented copolymers were tested for mechanical properties by preparing a 10% solution of the copolymer in tetrahydrofuran or 50/50 toluene/isopropanol and pouring the solution into a Petri dish. The solvent was allowed to evaporate to produce films from about 0.4 to 1.5 mm thick.
Mechanical testing was performed on an INSTRON(trademark) Model 1122 tensile tester. Testing was performed according to a modification of ASTM D412-83. Samples were prepared according to Method B (cut ring specimens). Type 1 rings (5.1 cm circumference) were produced with a specially-designed precision ring cutter. The INSTRON(trademark) analog output signal was routed to a digital voltmeter with accuracy better than 0.5% and the digital readings were recorded by a computer. Modifications to the ASTM test were as follows: the crosshead speed was 12.7 cm/mn; the test fixture shafts (upper and lower jaw) rotated At 30 rpm in the same direction to maintain uniform strain throughout the entire ring. Modulus, maximum stress and elongation at break were then calculated.